Liquid electro-photographic (LEP) printing uses a special kind of ink to form images on paper or other print medium. LEP ink, which is sometimes referred to as liquid toner, includes colorant and toner particles dispersed in a carrier liquid. The LEP printing process involves placing an electrostatic charge pattern of the desired printed image on a photoconductor and developing the image by applying a thin layer of ink to the charged photoconductor. Charged particles in the ink cause the ink to adhere to the pattern of the desired image on the photoconductor. The ink pattern is transferred from the photoconductor to an intermediate transfer member and then from the intermediate transfer member to the paper or other printable medium.
The thin layer of ink is applied to the photoconductor with a roller, typically referred to as a developer roller. The developer roller is part of a replaceable image developer unit that also includes parts that reclaim clean and reclaim residual ink from the developer roller. Residual ink is removed from the developer roller electrically using a charged cleaning roller that rotates along the developer roller. Ink is scraped off the cleaning roller with a wiper blade and, after scraping, the surface of the cleaning roller is scrubbed with a so-called “sponge” roller that rotates against the cleaning roller. The wiper blade wears down and often scratches the cleaning roller, resulting in “banding” and other defects in the printed image that ultimately lead to replacing the developer unit. The wiper's adverse affect on print quality is particularly evident in some newer inks used in LEP printers.